1. Field of the Invention
The present invention relates to a standardized mechanical interface (SMIF) container for transferring workpieces such as reticles in a semiconductor or reticle fab, and in particular to a container including a static dissipative support structure mounted to the container shell and grounded to the container door for dissipating static electric charge from contact points on the top side of the reticle.
2. Description of the Related Art
Semiconductor devices are made up of as many as fifty individual patterned layers of silicon, silicon compounds and metals. During fabrication of these devices, the pattern for each of these layers is contained on a mask called a reticle. A reticle is an optically clear quartz substrate on which a pattern has been formed by photolithography or other such processes. In particular, a layer of photoresist is applied on a chrome coated reticle blank. Thereafter, the pattern for a particular layer to be formed on a semiconductor wafer is transferred onto the reticle as for example by a laser pattern generator or e-beam. After pattern generation on the photoresist, the exposed portions of the photoresist are removed to leave the unwanted portions of the chrome layer exposed. These unwanted portions are then etched away. The remaining photoresist is then removed in a process which leaves the clean pattern on the surface on the reticle.
In order to keep the surface of the reticle clean, a thin transparent sheet called a pellicle is mounted a short distance away from the surface of the reticle containing the pattern. This ensures that any microscopic dust that settles on the reticle will be out of focus during the exposure process so as not to affect the pattern formed on the silicon wafer.
During fabrication of the reticle, it is important to minimize airborne particle fluxes onto the surface of the reticle on which the pattern is being formed, as any such particles can corrupt the pattern. Even after formation of the pattern and affixation of the pellicle, larger, or macro, contaminants can settle on the reticle which can interfere with pattern transference onto the semiconductor wafer. It would therefore be advantageous to shield the reticles from the external environment during reticle fabrication, during transfer of the reticle from the reticle fab to the semiconductor fab, and during usage of the reticle in the semiconductor fab.
In addition to exposing the reticle to airborne particulates, physical handling of a reticle during transfer can also damage a reticle. Common causes of damage when handling reticles include scratches, electrostatic discharge onto the reticle, and cracking of the reticle and/or pellicle.
In a semiconductor wafer fab, it is therefore known to store and transfer workpieces such as semiconductor wafers using a standard mechanical interface, or SMIF, system. The SMIF system was developed by the Hewlett-Packard Company and disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto workpieces such as reticles and semiconductor wafers during storage and transport of the workpieces through the fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the workpieces is essentially stationary relative to the workpieces and by ensuring that particles from the ambient environment do not enter the immediate workpiece environment.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
A SMIF system has three main components: (1) sealed containers, having a minimal volume, used for storing and transporting workpieces and/or cassettes which hold the workpieces; (2) enclosures placed over access ports and workpiece processing areas of processing equipment so that the environments inside the containers and enclosures (after having clean air sources) become miniature clean spaces; and (3) a transfer mechanism to load/unload workpieces and/or workpiece cassettes from a sealed container without contamination of the workpieces from external environments.
Electrostatic buildup on and discharge from reticles can damage or destroy the reticles, and concern about electrostatic damage has been increasing in recent years as device geometries get finer and the requirements for reliability become more stringent. In conventional SMIF pods, it is known to have conductive contacts on the reticle support in the pod door to dissipate electrostatic charge from the bottom surface of the reticle. The charge is then grounded through the pod door. Similarly, conductive contacts are provided on the reticle retainer in the pod shell to dissipate electrostatic charge from the top surface of the reticle. The charge from the top surface is then grounded through the pod shell.
A drawback to conventional reticle containers is that the shell must include static dissipative materials to provide a path to ground for the static charge from the top surface of the reticle. It is desirable that the shell be transparent so that the reticle can be viewed from the outside. However, the agents that make the shell statically dissipative cloud the shell and reduce its transparency.
The invention solves the drawbacks of prior reticle containers by providing a conductive path between the reticle retainer and the reticle supports. This allows electrostatic charge to be dissipated from the top surface of the reticle without the use of static dissipative materials in the pod shell. Since there is no need for static dissipative materials in the pod shell, the pod shell may be transparent to allow the viewing of the reticle within the reticle container.
In an embodiment, an apparatus for supporting an object within a SMIF pod, comprises a first support structure and a second support structure for supporting the object; and a retaining structure. The retaining structure includes first and second tabs for engaging the first and second support structures, respectively, to create a discharge path between the retaining structure and the first and second support structures. The retaining structure further includes means for preventing movement of the object within the SMIF pod during SMIF pod transport.
In a further embodiment, the first and second support structures are mechanically interconnected with a SMIF pod door. In an embodiment, the retaining structure is mechanically interconnected with a SMIF pod shell. In an additional embodiment, the first and second support structures and the retaining structure are formed of a substantially rigid, low particulating and electrostatically dissipative material.
In an alternate embodiment, an apparatus for supporting an object within a SMIF pod comprises at least two support structures mechanically interconnected with the SMIF pod door for supporting the object; and at least one retaining structure mechanically interconnected with the SMIF pod shell. Each retaining structure has a first tab and a second tab for engaging the support structures when the SMIF pod shell forms a seal with the SMIF pod door. This creates a discharge path between the support structures and the retaining structure, and further preventing movement of the object within the SMIF pod during SMIF pod transport. In a further embodiment, the support structures and the retaining structure are formed of a substantially rigid, low particulating and electrostatically dissipative material.
In yet another embodiment, a SMIF pod for supporting an object comprises a pod door having an interior surface having at least two electrically conductive columns mechanically interconnected with the interior surface to support the object. The SMIF pod also comprises a pod shell with an interior surface having at least one electrically conductive arm mechanically interconnected with the interior surface and having tabs for engaging the columns. The SMIF pod further comprises a discharge path, which is created between the column and the arm when the pod shell engages the pod door. In a further embodiment, the arm retains the object when the pod shell engages the pod door. In an additional embodiment, the column and the arm are formed of a substantially rigid, low particulating and electrostatically dissipative material.
In yet another embodiment, a SMIF pod for supporting an object comprises a pod door having an interior surface with four electrically conductive columns. The four electrically conductive columns are mechanically interconnected with the interior surface to support the object. The SMIF pod further comprises a pod shell having an interior surface with electrically conductive arms. The electrically conductive arms are mechanically interconnected with the interior surface. Each arm has a first and second tab, which create a discharge path between the columns and the arms when the first and second tabs of each arm engage the columns.
In a further embodiment, the arms further retain the object when the pod shell engages the pod door. In a further embodiment, the columns further remove electrostatic charges from a bottom surface of the object. In a further embodiment, the arms remove electrostatic charges from a top surface of the object. In a further embodiment, the columns and the arms are formed of a substantially rigid, low particulating and electrostatically dissipative material.
In an alternate embodiment, a SMIF pod for supporting an object comprises a pod door having an interior surface with four electrically conductive columns mechanically interconnected with the interior surface to support the object and further removing electrostatic charges from a bottom surface of the object. The SMIF pod further comprises a pod shell having an interior surface with electrically conductive arms mechanically interconnected with the interior surface. Each arm has a first and second tab, and further removes electrostatic charges from a top surface of the object. The SMIF pod further comprises a discharge path, which is created between the columns and the arms when the first and second tabs of each arm engages the columns.